1. Field of the Invention
This invention relates to the production of solid state devices by the etching of semiconductor materials and oxides.
2. Description of the Prior Art
In the production of solid state devices, including semiconductor devices, one nearly universal step is the etching of a semiconductor material or an oxide. One use of an etch is to remove native oxide material that naturally forms on a semiconductor upon exposure to air. In another use, semiconductor material is etched to improve its smoothness and to remove defects in the surface. In still another use, a patterned layer is etched in a semiconductor or a protective material thereon. For example, a semiconductor is etched wherein the unetched region is protected by a patterned oxide layer. Conversely, an oxide layer may be selectively etched wherein the unetched oxide is protected by a patterned layer of resist material.
In the past, most etching operations have been accomplished by the use of a liquid etchant. Typical liquid etchants include halogens in solution, including for example, HF, HCL, Br.sub.2, I.sub.2, etc. However, in current semiconductor device production, the trend is towards dry plasma etching methods, typically wherein an ionized species is responsible for, or contributes to, the etching operation. Plasma etching atmospheres typically also comprise halogens or halogen-containing compounds, such as CF.sub.4, SF.sub.6, etc. Dry etching atmospheres have various advantages oven liquid etchants, including for example, improved anisotropy of the etch, and the ability to be more easily automated along a continuous production line. An overview of current etching compositions, both liquid and plasma, is given in "Chemical Etching of Silicon, Germanium, Gallium Arsenide, and Gallium Phosphide", by W. Kern, in the RCA Review, Vol. 39, at page 278 (1978).
One of the current problems in semiconductor manufacturing processes is the selective dry etching of oxides of III-V compound semiconductor material, such as GaAs oxide, InP oxide, etc. In particular, typical prior art etchants preferentially etch the semiconductor material as compared to its oxide. Therefore, if the patterned oxide on a III-V compound semiconductor is etched, severe undercutting typically occurs under portions of the oxide layer. One method of forming patterns of III-V oxides on III-V semiconductor substrates is by first forming a protective layer, typically SiO.sub.2 or Si.sub.3 N.sub.4, that can be selectively etched compared to the substrate. The III-V material is then oxidized in regions from which the protective layer has been removed; see U.S. Pat. No. 4,227,975, assigned to the same assignee as the present invention. However, it is desirable in many cases to selectively etch the patterned III-V oxide directly, avoiding extra processing steps. Furthermore, it is desirable to have a dry etching technique for removing the native oxides on III-V compound semiconductor material that form upon exposure to the atmosphere prior to other processing steps.
In processing silicon semiconductor devices, it is frequently necessary to etch the silicon preferentially to a silicon dioxide or silicon nitride patterned layer overlying the silicon. This need arises, for example, when forming polycrystalline silicon sense lines in memory integrated circuits, logic circuits, etc. While certain etchants, including plasma etchants, are known to be capable of etching silicon preferentially to silicon dioxide and silicon nitride, it is desirable to find additional etchants for this purpose.
The use of H.sub.2 gas in conjunction with halocarbon compounds in plasma etching atmospheres is known. The H.sub.2 gas typically forms a minor proportion of the atmosphere, typically less than 10 percent; see, for example, "Selective Etching of Silicon Dioxide Using Reactive Ion Etching With CF.sub.4 --H.sub.2 ", by L. M. Ephrath, in the Journal of the Electrochemical Society, page 1419 (1979). As practiced in the art, this technique calls for adding the H.sub.2 gas to reduce the etch rate of the silicon, while leaving the etch rate of the silicon dioxide or silicon nitride substantially unchanged in the presence of a halocarbon plasma atmosphere; see, for example, U.S. Pat. No. 3,940,506. This behavior is conventionally explained by stating that the hydrogen gas acts as a recombination center for fluorine ions, which preferentially attack silicon.
The use of a pure hydrogen plasma to erode silicon is a known phenomenon; see, for example, "Reactivity of Solid Silicon With Hydrogen Under Conditions of a Low Pressure Plasma", by A. P. Webb et al, in Chemical Physics Letters, Vol. 62, pages 173-177 (1979). However, this technique has not been widely adopted for semiconductor device use, perhaps because no selectivity of etching silicon with regards to silicon dioxide or silicon nitride, the common protective mask materials, has been shown. Atomic hydrogen has also been used to passivate defects produced in laser-annealed semiconductors under conditions in which substantially no etching is produced; see U.S. Patent application Ser. No. 98,398, filed Nov. 29, 1979, U.S. Pat. No. 4,266,986, assigned to the same assignee as the present invention.
For the above-noted reasons, it would be desirable to have a dry etching atmosphere that would selectively etch silicon in the presence of silicon dioxide or silicon nitride, and to etch the oxides of III-V compounds and/or the III-V materials themselves.